A Search for 6.7 Ghz Methanol Masers in M33
نویسندگان
چکیده
We report the negative results from a search for 6.7 GHz methanol masers in the nearby spiral galaxy M33. We observed 14 GMCs in the central 4 kpc of the Galaxy, and found 3σ upper limits to the flux density of ∼9 mJy in spectral channels having a velocity width of 0.069 kms. By velocity shifting and combining the spectra from the positions observed, we obtain an effective 3σ upper limit on the average emission of ∼1mJy in a 0.25 kms channel. These limits lie significantly below what we would expect based on our estimates of the methanol maser luminosity function in the Milky Way. The most likely explanation for the absence of detectable methanol masers appears to be the metallicity of M33, which is modestly less than that of the Milky Way. Subject headings: ISM: molecules – individual(methanol); ISM: masers; Galaxies (M33)
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